Trade Union Membership and the Free Rider Problem: the Role of Harassment Activities z Bruno Chiarini zyxwv Absfract. Although there exists an extensive titerature which uses econometric tech- niques to examine the process of unionisation in the industrial countries, a well established theory about the individual propensity to join the union zyx has still to be developed. We feel that the workers’ personal relationships in the working places impinge on their decision to unionise. To this end, we have set out a coercion model zy of trade union membership without compulsory membership, based on the rank and file union membes’ harassment activities. Union members use these unfriendly activities to eliminate the free-rider ploblem, encouraging unionisation and reducing the cost of joining a union. Intraduetiaa It is commonly assumed that union membership is affected by structural factors such as changes in labour legislation, the em- ployment structure and industrial relations (which explain the trend in union membership), and by macroeconomic conditions such as changes in unemployment, wages and prices. Although there exists an extensive literature which uses econometric techniques to examine the process of unionisation in industrial countries, an established theory about the individual propensity to join the union has still to developed (e.g. Grossman zyx 1983, Booth 1984). Recent expIanations of the decline in trade union density in the 1980s have not provided new clues (e.g. Carruth and Disney 1988, Disney 1990). Bruno Chiarini, University of Southampton. I would like to thank an anonymous referee for helpful comments. Received on February 11, 1992 and approved by the Editorial Board on May 19, JEL C72 1992. LABOUR 6 (2) 49-63 (1992)